The European honey bee, Apis mellifera, is vital to the pollination of agricultural and wild plants [1]. There is widespread concern about the worldwide decline in the abundance of A.meffifera [2]. The ectoparasitic Varroa mite (Varroa destructor) is the most important pest of A.meffifera and plays a central role to honey bee losses [3].
V.destructor originally parasitized the Asian bee (A.cerana) where it nearly exclusively parasitized the male bees (drones), thus making little impact on the bee colony the European honey bee (A.meffifera) upon which it parasitizes both the drones and female bees (workers). This shift in parasitized caste is significant because the workers make up the bulk of the adult bee population within a colony [4].
V.destructor entered mainland Europe in the 1970's, the USA in 1987 and the UK in 1992 and subsequently has been associated with the loss of millions of colonies [3]. The mite causes damage by feeding on the haemolymph of both the developing bee within brood cells and the adult bee, thus weakening the immune systems of their hosts. Moreover, wound sites caused by mite feeding harbour bacterial infections, such as Melissococcus pluton, and mites transmit viral pathogens such as deformed wing virus (DWV), Kashmir bee virus (KBV), acute bee paralysis virus (ABPV), and black queen cell virus (BQCV).
In terms of both the number of enterprises affected and the impact of global food production, varroosis is arguably the most serious disease of livestock in any species. Previous control of V.destructor by chemical treatment is increasingly ineffective due to the development of widespread resistance in mites to the limited available acaricides [5]. Thus, there is an urgent need to harness modern molecular techniques for research into the biology and, ultimately, the control of this non-model organism, V.destructor. 
RNA interference (RNAi) is a gene silencing technique that is becoming an ever more powerful tool in investigating the functional role of specific genes that may be potential targets for chemotherapeutic intervention. The RNAi mechanism involves the in vivo production of small interfering RNA molecules (siRNAs) from larger introduced double-stranded RNA (dsRNA). siRNA molecules target and destroy specific mRNA, silencing the target gene at the post-transcriptional stage.
Whyard et al. 2009 discuss the use of RNAi based gene suppression as a species-specific insecticide [6], with other studies showing that V.destructor is susceptible to the suppression of gene expression via the administration of dsRNA [7]. The dsRNA can be effectively delivered to V.destructor both directly, for example by via intrahaemocoelic injection or immersion/spraying in solutions containing dsRNA [7], or indirectly, for example by feeding dsRNA to A.meffifera hosts which are subsequently parasitized by the V.destructor mites [8], [9].
This transfer of dsRNA from A.meffifera hosts to V.destructor mites has been reported to lead to a decrease in mite population in tested mini-hives [9]. The authors report a maximum reduction in V.destructor mite numbers of 61%, as recorded at the end of a 60-day trial period during which mites were exposed to a dsRNA mix containing 14 V.destructor sequences. The 60-day trial period allowed for two reproductive cycles of V.destructor, and the authors of [9] did not directly measure V.destructor mite mortality; thus, the 61% figure represents the combined effects of mortality and reduced fecundity over two generations of V.destructor mite.